The present invention relates to a thin film magnetic head having an inductive magnetic head as a write head element and a magneto-resistance effect type head element as a read head element, both provided on a substrate. More specifically, the invention relates to a thin film magnetic head in which island-shaped rails are formed in a surface facing a recording medium, thereby causing the head to fly with respect to the recording medium.
In recent years, magnetic disk drives are becoming smaller in size and larger in capacity. Currently, small magnetic disk drives employing 3.5-inch and 2.5-inch disk-shaped recording media (hereinafter to be simply referred to as disks) have become main stream.
In the magnetic disk drive, the disk rotates at a low speed. Thus, when the inductive magnetic head of which a read output depends on a disk rotation speed is employed, the read output is reduced. On contrast therewith, in the magneto-resistance effect type head employing a magneto-resistance effect element which detects a change in resistance caused by a change in a magnetic field, thereby producing the read output, the read output does not depend on the rotation speed of the disk. Thus, even in the small magnetic disk drive, a high read output can be obtained.
Further, in the magneto-resistance effect type head, the read output that is higher than that with the inductive magnetic head can be obtained from narrower tracks as well, which are associated with a trend toward a higher recording density. Accordingly, the magneto-resistance effect type head can be conceived as a magnetic head suitable for achievement of smaller size and larger capacity.
In view of this fact, in the small magnetic disk drive, the thin film magnetic head having the inductive magnetic head as the write head element and the magneto-resistance effect type head as the read head element, in combination, is employed.
Among the magneto-resistance effect type heads are Anisotropic Magneto Resistive (AMR) heads that employ AMR elements, Giant Magneto Resistive (GMR) heads that employ GMR elements, and Tunneling Magneto Resistive heads that employ TMR elements. These are used in the form of the read head element for the thin-film magnetic head. These three types of magneto-resistance effect type heads will be generically referred to as MR head elements of the thin-film magnetic head, while the magnetic materials thereof will be referred to as MR elements.
In the MR head element, in order to obtain a change in the resistance of the MR element caused by a change in the magnetic field to achieve the highest read efficiency, the MR element should be exposed at the disk-facing surface of a magnetic head slider. This disk-facing surface will be hereinafter referred to as an air bearing surface.
In the MR head element having the MR element exposed at the air bearing surface thereof as described above, part of the MR element is also lapped during processing of the air bearing surface, thereby exposing the end of the MR element at the air bearing surface. In the write head element that writes data on the disk by means of a leakage flux as well, the leading ends of the upper and lower poles of the write head element are also lapped during processing of the air bearing surface, like the MR head element lapped, thereby exposing the ends of the write head element at the air bearing surface.
Generally, the thin-film magnetic head having the write head element and the read head element as described above is fabricated as follows:
First, an Al2O3 (alumina) layer having a film thickness of 2 to 10 μm is formed as an insulation film (to be referred to as base alumina) on a hard substrate made of a material such as Al2O3—TiC (alumina titanium carbide) or SIC (silicon carbide), and a shield layer, a gap layer, an MR element, the upper and lower poles of the write head element, a protective film of the alumina layer are laminated thereon in this stated order. This laminate structure is formed on a 5-inch substrate by thin film forming processing using lithography.
This substrate is cut into two-inch rectangular pieces (e.g. row bars) by means of a diamond grindstone, warps resulting from cutting are removed by a method such as double side lapping, and then one surface of the laminate structure on the substrate (or the end surfaces of the respective layers) is lapped with a high degree of accuracy, thereby forming the disk-facing air bearing surfaces.
Then, rails for generating a negative pressure to cause the respective thin film magnetic heads to fly from the surface of the disk are formed in the form of islands using a dry process such as ion milling. Then, after formation of the rails, small pieces (e.g. sliders) each including a laminate structure (e.g. a head element portion) is cut from the row bar, thereby completing thin film magnetic heads.
As a method of lapping the air bearing surfaces in the state of the row bar, there is employed a lapping method in which the row bar adhered to a lapping jig is pressed and slid while dropping a lapping slurry including lapping particles such as diamond onto a rotating circular plate made of a soft metal.
The thin film magnetic head is formed of composite materials constituted by soft metals such as parmalloy, alumina, and alumina titanium carbide. The soft metals are used for the MR head element as the read head element and the upper and lower poles of the inductive magnetic head element as the write head element in the head element portion, alumina is used for the insulating protective film, and alumina titanium carbide is used for a slider substrate member. Hardness varies among these materials. Thus, if lapping of the air bearing surface is performed, the head element portion that includes the MR head element, the upper and lower poles of the write head element, formed of the soft metals is recessed, thereby producing a recession in the air bearing surface.
This recession is referred to as a pole tip recession or a PTR. The pole tip recession is defined as a recession produced between the surface of the head element portion and the surface of a substrate member. The surface of the head element portion is constituted by the upper and lower shield layers and the magnetic film of the MR head element and the upper and lower poles of the write head element, formed of the soft metals. The surface of the substrate member is constituted by a hard ceramic such as Al2O3—TiC or SiC.
A recession produced between the surface of the head element portion and the insulating protective film formed of alumina is referred to as a pole recession, while a recession produced between the surface of the insulating protective film and the substrate member is referred to as the alumina recession. Accordingly, the pole tip recession is defined as the sum of the pole recession and the alumina recession.
On the other hand, in order to improve the areal density of the magnetic disk drive, it is essential to reduce a gap (a flying height) between the surface of the disk and the air bearing surface of the thin film magnetic head, thereby reducing magnetic spacing. The magnetic spacing is the distance between the MR head element and the write head element, exposed at the air bearing surface and the magnetic film surface of the disk. However, even if the flying height is reduced, the magnetic spacing will increase if the pole tip recession increases. Thus, in order to improve the areal density, a reduction in the pole tip recession is required.
Among the methods of reducing the pole tip recession, there is known the one described in JP-A-11-302636.
A surface 51 facing the disk (air bearing surface flying from the disk) of a thin film magnetic head slider 50 described therein has a configuration illustrated in FIG. 16. The air bearing surface 51 includes a convex portion 52 generally formed along three sides, and a concave portion 53 relative to the convex portion 52, which extends from the center of the air bearing surface 51 to one side of the air bearing surface 51. Air flows out from the side at both ends of the convex portion 52 (upper side in FIG. 16). Accordingly, when this air outflow end is used, the direction in which the head moves with respect to the disk, not illustrated, becomes vertical in the drawing. On one end of the concave portion 52 or on one side end of the air outflow side (air outflow end), a head element portion 54 that includes the write head element and the read head element is provided. With this arrangement, data recording on the disk and data reproduction from the disk are performed.
FIG. 17 is a diagram showing a vertical section of the slider 50 in a step of a thin film magnetic head manufacturing process. This is the cross section shown by the arrows XVII—XVII in FIG. 16.
In this step, the head element portion 54 protected by an insulation layer 56 is provided for a substrate 55, and the air bearing surface 51 that includes the surfaces of the head element section 54 and the substrate 55 is lapped.
As a material for the substrate 55, Al2O3—TiC (AlTic) is employed, while as the insulation layer 56, Al2O3 (alumina) is employed. Al2O3—TiC is harder than Al2O3. For this reason, when the air bearing surface 51 is lapped, the recession or the alumina recession of approximately 4-5 nm is produced between the surface of the substrate 55 and the surface of the insulation layer 56. Incidentally, since elements such as an MR head element 57, an upper pole 58 and a lower pole 59 of the write head element, and a lower shield layer 60 in the head element portion 54 have lower hardness than the insulation layer 56, a recession (a pole recession) is also produced between these elements in the head element portion 54 and the insulation layer 56. When the air bearing surface 51 is lapped, however, the alumina insulation layer 56 is chemically etched by an alkali slurry. Hence this reduces the pole recession between the insulation layer 56 and the head element portion 54 to substantially zero. The pole tip recession becomes therefore substantially equal to the alumina recession.
After the air bearing surface 51 configured as described above has been lapped, a mask 61 is provided for the surface of the insulation layer 56, and then the surface of the substrate 55 is etched, as illustrated in FIG. 18. With this arrangement, the surface of the insulation layer 56 and the surface of the substrate 55 in the air bearing surface 51 are disposed on the same plane, or the pole tip recession is reduced to zero. Alternatively, the surface of the insulation layer 56 protrudes more towards a disk 62 than the surface of the substrate 55. Then, a protective film 63 made of DLC is formed over the entire air bearing surface 51.
Since the thin film magnetic head is configured as described above, the following effects can be obtained. If the protective film 63 is provided without removing the alumina recession of 4-5 nm, as shown in FIG. 17, the flying height, which is defined as the minimum distance between the thin film magnetic head 50 and the disk 62 during the operation of the magnetic head drive as illustrated in FIG. 19 is determined by the surface of the substrate 55. The distance between the surface of the head element portion 54 and the magnetic film of the disk 62 (not shown) or the magnetic spacing (referred to as a “magnetic space” in JP-A-2001-236619) becomes larger than the flying height by the pole tip recession (being substantially equal to the alumina recession). However, as described in FIGS. 18 and 19, the pole tip recession is reduced to substantially zero. Thus, the magnetic spacing is correspondingly reduced, so that the read output is improved.
As illustrated in FIG. 2 and as will be described below in detail, there is known a thin film magnetic head, a disk-facing surface 3 of which has an island-shaped rail 10a in the center of an air outflow end 8, an island-shaped rail 10b at an air inflow end, and a head element portion 7 for the island-shaped rail 10a at the air outflow end. The island-shaped rail (center rail) 10a includes a center rail shallow groove surface 5a and a center rail flying surface 4a. The center rail shallow groove surface 5a protrudes from a deep groove surface 6 by a predetermined height, while the center rail flying surface 4a protrudes from the center rail shallow surface 5a by a predetermined height. The end surface of the head element portion 7 protected by a protective layer is exposed at the center rail flying surface 4a. 
The island-shaped rail (air inflow end rail) 10b includes an air inflow end rail shallow groove surface 5b and air inflow end rail flying surfaces 4b and 4c. The air inflow end rail shallow groove surface 5b is disposed along an air inflow end 9 and protrudes from the deep groove surface 6 by a predetermined height. The air inflow end rail flying surfaces 4b and 4c protrude from both ends of the air inflow rail shallow groove surface 5b by a predetermined height.
Since the thin film magnetic head has a shallow groove 5 between an air bearing surface 4 and the deep groove surface 6, and the island-shaped rails 10a and 10b constitute a slider with a two-step configuration, it is also referred to as a shallow dual step sub ambient slider.
In the manufacturing process of the thin film magnetic head as well, during lapping of the disk-facing surface 3, a pole tip recession is produced between the surface of a substrate and the surface of the protective layer that protects the head element portion 7, so that the magnetic spacing increases by the amount of the pole tip recession.
Then, in order to reduce the magnetic spacing, it was conceived that by using the technique described in JP-A-2001-236619, the surface of the substrate on the center rail flying surface 4a is also made to be the center rail shallow groove surface 5a and only a small region including the head element portion 7 is made to be the center rail flying surface 4a. 
However, this brings about a change in the proportions of the center rail flying surface 4a and the center rail shallow groove surface 5a in the disk-facing surface, thereby producing variations in the flying height. A desired flying height cannot be thereby obtained consistently.
The object of the present invention is therefore to solve the problems described above and to provide a thin film magnetic head that has a configuration of a shallow dual step sub ambient slider and can reduce a pole tip recession, thereby allowing an improvement in magnetic spacing.